1. Field of the Invention
This invention relates to an electrically operated power steering controller for controlling the operation of an electric motor for generating auxiliary steering torque and an adjusting method of its driving electric current offset.
2. Background Art
The electrically operated power steering controller disclosed in FIG. 2 of JP08-175405A includes an offset correcting means as well as a target signal generating means, an electric current detecting means and a drive control means. This electrically operated power steering controller controls the operation of the electric motor for generating the auxiliary steering torque. The target signal generating means calculates a driving electric current target value with respect to the electric motor, and generates a driving electric current target signal representing this driving electric current target value. The electric current detecting means detects the driving electric current value of the electric motor, and generates a driving electric current detecting signal representing this driving electric current value.
In this electrically operated power steering controller, the driving electric current of the electric motor is basically controlled by the driving control means such that the deviation between the driving electric current target value calculated by the target signal generating means and the driving electric current value detected by the electric current detecting means is zero. However, in the electrically operated power steering controller, the driving electric current value detected from the electric motor includes a driving electric current offset value even when the driving electric current target value with respect to the electric motor is zero. Therefore, the offset correcting means disclosed in the above prior art stores the driving electric current offset value when this driving electric current target value is zero, and makes an offset correction in consideration of this driving electric current offset value.
However, the offset correcting means disclosed in the above prior art stores the driving electric current offset value by using an output from the electric current detecting means for detecting the driving electric current value from the electric motor as it is. However, this electric current detecting means is a mass-produced product assembled into the electrically operated power steering controller, and its electric current detecting accuracy cannot be set to be so high from the restriction of cost. Therefore, the accuracy of the stored driving electric current offset value becomes low so that the accuracy of the offset correction also becomes low.